Anti-tip system for a power wheelchair

Abstract

An anti-tip system is provided for improving the stability of a powered vehicle, such as a powered wheelchair. The vehicle includes a drive-train assembly pivotally mounted to a main structural frame. A suspension system biases the drive-train assembly and its connected anti-tip wheel to a predetermined resting position. The drive-train assembly bi-directionally rotates about a pivot in response to torque applied to or acceleration forces on the vehicle. A linkage arrangement is provided and is characterized by a suspension arm pivotally mounting to the main structural frame about a pivot at one end thereof and an anti-tip wheel at the other end. The linkage may further include at least one link operable to transfer the bi-directional displacement of the drive-train assembly to the suspension arm. The link may include a bell crank member and/or may be resiliently compressible.

What is claimed is: 
     
       1. A wheelchair comprising:
 a frame; 
 a pair of drive wheels defining a drive wheel axis; 
 a drive assembly operatively coupled to at least one drive wheel of the pair of drive wheels, the drive assembly configured to rotate the at least one drive wheel about the drive wheel axis to thereby cause the wheelchair to move relative to a surface that defines a ground plane; 
 an arm pivotably mounted to the frame at an arm pivot axis; and 
 a caster wheel coupled to the arm, the caster wheel defining a rotational axis about which the caster wheel rotates, 
 wherein the vertical position of the arm pivot axis with respect to the ground plane when the caster wheel and the drive wheel are in contact with the surface is spaced from and positioned relatively below a straight line drawn between the drive wheel axis and the rotational axis of the caster wheel, and 
 wherein the arm is operatively coupled to the drive assembly such that the arm is configured to pivot about the arm pivot axis in response to torque created by rotation of the at least one drive wheel by the drive assembly so as to cause a responsive vertical movement of the caster wheel. 
 
     
     
       2. The wheelchair of  claim 1 , wherein the drive assembly is pivotally coupled to the frame at a drive assembly pivot axis that is substantially vertically aligned with the arm pivot axis. 
     
     
       3. The wheelchair of  claim 2 , further comprising a suspension link connecting the drive assembly to the arm, the suspension link operatively transferring motion of the drive assembly to the arm to cause the arm to rotate about its pivotal mounting in response to the torque created in rotation of the drive wheels. 
     
     
       4. The wheelchair of  claim 1 , wherein the caster wheel is a front caster wheel. 
     
     
       5. The wheelchair of  claim 1 , wherein the arm is configured to pivot about the arm pivot axis in response to braking so as to cause the caster wheel to apply a force to the surface. 
     
     
       6. The wheelchair of  claim 1 , wherein the suspension arm is configured to pivot about the suspension arm pivot axis to enable the caster wheel to move downwardly and engage a surface that is lower than the ground plane in response to braking 
     
     
       7. A wheelchair comprising:
 a frame; 
 a pair of drive wheels defining a drive wheel axis; 
 a drive assembly operatively coupled to at least one drive wheel of the pair of drive wheels, the drive assembly configured to provide power to the at least one drive wheel to rotate the drive wheel about the drive wheel axis to thereby cause the wheelchair to move relative to a surface that defines a ground plane; 
 an arm pivotably mounted to the frame at an arm pivot axis; and 
 a caster wheel coupled to the arm, the caster wheel defining a rotational axis about which the caster wheel rotates, 
 wherein the vertical position of the arm pivot axis with respect to the ground plane when the caster wheel and drive wheel are in contact with the surface is spaced from and positioned relatively below a straight line drawn between the drive wheel axis and the rotational axis of the caster wheel, and 
 wherein the arm is operatively coupled to the drive assembly such that (i) the arm is configured to pivot about the arm pivot axis in response to torque created by rotation of the at least one drive wheel by the drive, and (ii) the arm is configured to pivot about the arm pivot axis in response to braking 
 
     
     
       8. The wheelchair of  claim 7 , wherein the caster wheel is a front caster wheel and the arm is configured to pivot about the arm pivot axis in response to torque created by forward rotation of the at least one drive wheel by the drive assembly so as to cause a responsive vertically upward movement of the caster wheel. 
     
     
       9. The wheelchair of  claim 7 , wherein the drive assembly is pivotally coupled to the frame at a drive assembly pivot axis that is substantially vertically aligned with the arm pivot axis. 
     
     
       10. The wheelchair of  claim 9 , further comprising a suspension link connecting the drive assembly to the arm, the suspension link operatively transferring to the arm, motion of the drive assembly about its pivotal mounting in response to the torque created in rotation of the drive wheels. 
     
     
       11. The wheelchair of  claim 7 , wherein the caster wheel is a front caster wheel. 
     
     
       12. The wheelchair of  claim 7 , wherein the arm is configured to pivot about the arm pivot axis in response to braking torque so as to cause the caster wheel to apply a force to the surface. 
     
     
       13. The wheelchair of  claim 7 , wherein the arm is configured to pivot about the arm pivot axis so as to enable the caster wheel to move downwardly and engage a surface that is lower than the ground plane in response to braking.